Transmission-guard system and method for an inductive power supply

ABSTRACT

Wireless power transfer between a power transmitter and a power receiver may include a power transfer established by a detector of the wireless power transmitter detecting a magnetic field from a wireless power receiver in proximity to the wireless power transmitter and activating the wireless power transmitter to transfer power to the wireless power receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/883,457 filed Sep. 16, 2010, which is a continuation of PCTapplication Serial No. PCT/IL2008/001641 filed Dec. 18, 2008, whichclaims the benefit of U.S. provisional application Ser. Nos. 61/064,618filed Mar. 17, 2008, 61/071,151 filed Apr. 15, 2008, 61/129,526 filedJul. 2, 2008, 61/129,859 filed Jul. 24, 2008 and 61/129,970 filed Aug.4, 2008, the disclosures of which are hereby incorporated in theirentirety by reference herein.

TECHNICAL FIELD

The present invention is directed to inductive electrical powertransfer. More specifically, the present invention relates to providinga transmission guard for preventing an inductive power outlets fromtransmitting power in the absence of an inductive power receiver.

BACKGROUND

Inductive power coupling, as known in the art, allows energy to betransferred from a power supply to an electric load without connectingwires. A power supply is wired to a primary coil and an oscillatingelectric potential is applied across the primary coil, thereby inducingan oscillating magnetic field. The oscillating magnetic field may inducean oscillating electrical current in a secondary coil placed close tothe primary coil. In this way, electrical energy may be transmitted fromthe primary coil to the secondary coil by electromagnetic inductionwithout the two coils being conductively connected. When electricalenergy is transferred from a primary coil to a secondary coil the coilpair are said to be inductively coupled. An electric load wired inseries with such a secondary coil may draw energy from the power sourcewired to the primary coil when the secondary coil is inductively coupledthereto.

Induction type power outlets may be preferred to the more commonconductive power sockets because they provide seamless powertransmission and minimize the need for trailing wires.

Low power inductive electrical power transmission systems have beenproposed. One such example is described in U.S. Pat. No. 7,164,255 toHui. In Hui's system a planar inductive battery charging arrangementenables electronic devices to be charged. The system includes a planarcharging module having a charging surface on which a device to becharged is placed. Within the charging module, and parallel to thecharging surface, at least one, and preferably an array of primarywindings are provided. The primary windings inductively couple withsecondary windings within the device to be charged.

Such systems provide inductive coupling at relatively low power adequatefor charging batteries. It will be appreciated however, that base unitssuch as Hui's charging surface which transmit energy continuously, in alargely uniform manner over an extended area, are not suitable for usewith high energy systems, such as those required to power computers,light bulbs, televisions and the like.

Energy losses associated with high power inductive transfer systems aretypically larger than those in low power systems such as Hui's chargingsurface. In addition whereas in low power systems excess heat may bereadily dissipated, an uncoupled high power primary coil or itssurroundings may become dangerously hot.

Moreover, the oscillating voltage in a high power primary coil producesa oscillating magnetic field. Where a secondary coil is inductivelycoupled to the primary coil, the resulting flux linkage causes power tobe drawn by the secondary coil. Where there is no secondary coil to drawthe power, the oscillating magnetic field causes high energyelectromagnetic waves to be radiated in all directions which may haveundesired side affects, such as erasing data from credit cards and maybe harmful to bystanders particularly to those with pacemakers.

U.S. Pat. No. 6,803,744, to Sabo, titled “Alignment independent and selfaligning inductive power transfer system” describes an inductive powertransfer device for recharging cordless appliances. Sabo's deviceincludes a plurality of inductors which serve as the primary coil of atransformer. The secondary coil of the transformer is arranged withinthe appliance. When the appliance is positioned proximate to the powertransfer device with the respective coils in alignment, power isinductively transferred from the device to the appliance via thetransformer.

The inductors of Sabo's system are arranged in an array and connected toa power supply via switches which are selectively operable to activatethe respective inductors. These selectively operable switches areprovided to conserve power and to eliminate objectionableelectromagnetic fields. '744 thus indicates the problem ofelectromagnetic leakage as well as the need for each primary coil to beenergized from the power supply only when a secondary coil is withineffective range. Furthermore the power receiving units described in '744are bulky and impractical for use with small electrical devices.

The need remains therefore for a practical inductive power transfersystem for safely and conveniently delivering power wirelessly frominductive power outlets to inductive power receivers in an energyefficient manner. The present invention addresses this need.

SUMMARY

It is an aim of the invention to provide a transmission systemcomprising at least one inductive power outlet for transferring powerinductively to at least one inductive power receiver, at least onealignment mechanism for aligning the power receiver to the power outletand at least one signal transfer system for passing control signals fromthe power receiver to the power outlet. Typically, the inductive poweroutlet comprises at least one primary inductive coil wired to a powersource via a driver, the driver for providing an oscillating voltageacross the primary inductive coil at high frequency, and a primaryferromagnetic core. The inductive power receiver comprises at least onesecondary inductive coil for coupling with the primary inductive coil,the secondary inductive coil being wired to a power regulator. Thesignal transfer system comprises a signal emitter associated with thepower receiver and a signal detector associated with the power outlet.

Optionally, the alignment mechanism comprises a first element associatedwith the power outlet and a second magnetic element associated with thepower receiver. Typically, the signal emitter comprises an opticalemitter and the signal detector comprises an optical detector.Optionally, again, the power regulator comprises a rectifier forconverting an AC input from the inductive power outlet into a DC outputfor powering the electrical device. Another aim of the invention is topresent an inductive power receiver for receiving power inductively froman inductive power outlet. Optionally, the system comprises a powerconverter selected from the group comprising: a transformer, a DC-to-DCconverter, an AC-to-DC converter, an AC-to-AC converter, a flybacktransformer, a flyback converter, a full-bridge converter, a half-bridgeconverter and a forward converter.

A further aim of the invention is to present an inductive power transfersystem comprising at least one inductive power outlet for transferringpower inductively to at least one inductive power receiver, theinductive power outlet comprising at least one primary inductor wired toa power source via a driver, and the inductive power receiver comprisingat least one secondary inductor for coupling with the primary inductor,the secondary inductor for providing power to an electric load; theinductive power transfer system comprising a low heat-loss full waverectifier comprising: a first half-wave rectifier having one anode wiredto a first output terminal and one cathode wired to a first inputterminal; a second half-wave rectifier having one anode wired to thefirst output terminal and one cathode wired to a second input terminal;a third half-wave rectifier having one anode wired to the first inputterminal and one cathode wired to a second output terminal, and a fourthhalf-wave rectifier having one anode wired to the second input terminaland one cathode wired to the second output terminal; the full waverectifier for providing an output of constant polarity from an input ofvariable polarity, wherein at least one half-wave rectifier comprises anelectronic switch configured to be in its ON state when the currentflowing through the cathode of the switch exceeds a predeterminedthreshold.

Optionally, the first half-wave rectifiers comprises a first electronicswitch configured to be in its ON setting when the current flowingthrough its cathode exceeds a first predetermined threshold, and thesecond half-wave rectifiers comprises a second electronic switchconfigured to be in its ON setting when the current flowing through itscathode exceeds a second predetermined threshold. Preferably, at leastone half-wave rectifier comprises an electronic switch configured to beswitched between it's ON and OFF states in synchrony with the frequencyof the input signal.

Preferably, the first half-wave rectifier comprises a first electronicswitch configured to be in its ON state when the current flowing throughits cathode exceeds a predetermined threshold; the second half-waverectifiers comprises a second electronic switch configured to be in itsON state when the current flowing through its cathode exceeds apredetermined threshold; the third half-wave rectifiers comprises athird electronic switch configured to be switched between its ON and OFFstates in phase with the voltage signal at the second input terminal,and the fourth half-wave rectifiers comprises a third electronic switchconfigured to be switched between its ON and OFF states in phase withthe voltage signal at the first input terminal.

Typically the electronic switch comprises a transistor, in particular, aMOSFET device. Preferably, the electronic switch comprises: a MOSFETdevice comprising a source terminal, a drain terminal and a gateterminal; a half-wave rectifier wired to the source terminal and thedrain terminal in parallel with the MOSFET device, and a current monitorconfigured to monitor a drain-current flowing through the drain terminaland to send a gate signal to the gate terminal such that the MOSFET isswitched to its ON state when the drain-current exceeds a firstthreshold current and the MOSFET is switched to its OFF state when thedrain-current falls below a second threshold current. Optionally, thecurrent monitor comprises a current transformer.

It is another aim of the invention to present an inductive powertransfer system comprising at least one inductive power outletcomprising at least one primary inductive coil wired to a power supplyvia a driver; the primary inductive coil for forming an inductive couplewith at least one secondary inductive coil wired to an electric load,the secondary inductive coil associated with an inductive power receiverwherein the driver is configured to provide a driving voltage across theprimary inductive coil, the driving voltage oscillating at atransmission frequency significantly different from the resonantfrequency of the inductive couple. Optionally, the driver comprises aswitching unit for intermittently connecting the primary inductive coilto the power supply.

Preferably, the transmission frequency lies within a range in whichinduced voltage varies approximately linearly with frequency.Optionally, the driver is configured to adjust the transmissionfrequency in response to the feedback signals.

Optionally, the inductive power outlet comprising a signal detectoradapted to detect a first signal and a second signal, and the driver isconfigured to: increase the transmission frequency when the first signalis detected by the detector, and decrease the transmission frequencywhen the second signal is detected by the detector. The feedback signalsgenerally carry data pertaining to the operational parameters of theelectric load. Operational parameters are selected from the groupcomprising: required operating voltage for the electric load; requiredoperating current for the electric load; required operating temperaturefor the electric load; required operating power for the electric load;measured operating voltage for the electric load; measured operatingcurrent for the electric load; measured operating temperature for theelectric load; measured operating power for the electric load; powerdelivered to the primary inductive coil; power received by the secondaryinductive coil, and a user identification code. Optionally, the detectoris selected from the list comprising optical detectors, radio receivers,audio detectors and voltage peak detectors.

Preferably, the driver further comprises a voltage monitor formonitoring the amplitude of a primary voltage across the primary coil.Optionally, the voltage monitor is configured to detect significantincreases in primary voltage.

In preferred embodiments, the driving voltage oscillating at atransmission frequency higher than the resonant frequency of theinductive couple, wherein the primary inductive coil is further wired toa reception circuit comprising a voltage monitor for monitoring theamplitude of a primary voltage across the primary coil, and thesecondary inductive coil is further wired to a transmission circuit forconnecting at least one electric element to the secondary inductive coilthereby increasing the resonant frequency such that a control signal maybe transferred from the transmission circuit to the reception circuit.Optionally, the secondary inductive coil is wired to two inputs of abridge rectifier and the electric load is wired to two outputs of thebridge rectifier wherein the transmission circuit is wired to one inputof the bridge rectifier and one output of the bridge rectifier.Typically, the transmission circuit further comprises a modulator formodulating a bit-rate signal with an input signal to create a modulatedsignal and a switch for intermittently connecting the electrical elementto the secondary inductive coil according to the modulated signal.Optionally, the voltage monitor further comprises a correlator forcross-correlating the amplitude of the primary voltage with the bit-ratesignal for producing an output signal.

In certain embodiments, the control signal is for transferring afeedback signal from the secondary inductive coil to the primaryinductive coil for regulating power transfer across an inductive powercoupling. The driver may be configured to adjust the transmissionfrequency in response to the feedback signals. Typically, the system isadapted to transfer a first signal and a second signal, and the driveris configured to: increase the transmission frequency when the firstsignal is received by the receiver, and decrease the transmissionfrequency when the second signal is received by the receiver.

It is still a further aim of the invention to present an inductive poweradaptor comprising: at least one inductive power receiver for receivingpower from an inductive power outlet; at least one power connector forconductively connecting the power receiver to at least one electricaldevice, and a grip for handling the adapter, the grip being thermallyisolated from the power receiver such that when the power receiver is inoperation a user may handle the adapter without injury. Optionally, theadapter further comprises a printed circuit board.

Typically, the power receiver is for providing power at a rate above 50W. Preferably, the adapter comprises a cooling system for dissipatingheat generated therein. Optionally, the cooling system comprises atleast one air outlet, situated above the power receiver, and at leastone air inlet, situated below the power receiver such that hot airheated by the power receiver flows out of the adapter through the airoutlet and cool air from outside is drawn into the adapter through theair inlets.

Preferably, the adapter further comprises at least one heat sink fordissipating heat generated by the power receiver. Optionally, the heatsink is a metallic disk. Typically, the heat sink is smaller than theinternal diameter of a casing of the adapter thereby allowing air tocirculate between the heat sink and the casing.

It is a further aim of the invention to present a transmission-guard forpreventing an inductive power outlet from transmitting power in theabsence of an electric load inductively coupled thereto, the inductivepower outlet comprising at least one primary coil connectable to a powersupply, for inductively coupling with a secondary coil wired to theelectric load, the transmission-guard comprising at least onetransmission-lock for preventing the primary coil from connecting to thepower supply in the absence of a transmission-key.

Optionally, the transmission-lock comprises at least one magnetic switchand the transmission-key comprises at least one magnetic elementassociated with the secondary coil. Typically, the transmission-lockcomprises an array of magnetic switches configured to connect theprimary coil to the power supply only when activated by a matchingconfiguration of magnetic elements. Optionally, the magnetic switchcomprises a magnetic sensor.

Alternatively, the transmission-guard comprises: at least one emitterfor emitting a release-signal, and at least one detector for detectingthe release signal; the transmission-key comprises at least one bridgeassociated with the secondary coil for bridging between the at least oneemitter and the at least one detector, such that when the secondary coilis brought into alignment with the primary coil the release signal isguided from the emitter to the detector. Optionally, the release-signalis an optical signal and the bridge comprises at least one opticalwave-guide. Alternatively, the release-signal is a magnetic signal andthe bridge comprises a magnetic flux guide. In other embodiments thetransmission-key comprises a release-signal emitted by an emitterassociated with the secondary coil. The release-signal may be an opticalsignal and the optical signal may be an infra-red pulse received by anoptical detector configured to release the transmission-lock.Alternatively the release-signal is a magnetic signal. In someembodiments of the transmission guard the emitter is the secondary coil.

Optionally, the transmission-guard comprises a low-power power pulsetransmitted by the primary coil, such that when the secondary coil isaligned to the primary coil the power pulse is transferred to thesecondary coil and the transmission-key is triggered by the power pulse.Preferably, a first transmission-lock is released by a firsttransmission-key indicating the probable presence of a secondary coiland a second transmission-lock is released by a second transmission-keyconfirming the presence of the secondary coil. The firsttransmission-lock may initiate a power pulse transmitted from theprimary coil, and the second transmission key being triggered by thepower pulse being received by the secondary coil. The magnetic elementmay comprise a ferrite flux guidance core. Variously, the release-signalis selected from the group comprising: mechanical signals, audiosignals, ultra-sonic signals and microwaves. It is also an aim topresent separately: a transmission-key for use in thetransmission-guard, a transmission-lock for use in thetransmission-guard, and an inductive power outlet protected by thetransmission-guard.

It is yet another aim of the invention to present an inductive powertransfer system comprising at least one inductive power receiver forreceiving power from an inductive power outlet, the inductive poweroutlet comprising at least one primary inductor wired to a power sourcevia a driver, and the inductive power receiver comprising at least onesecondary inductor for coupling with the primary inductor, the secondaryinductor for providing power to an electric load; the inductive powertransfer system comprising at least one magnetic flux guide fordirecting magnetic flux from the primary inductor to the secondaryinductor wherein the magnetic flux guide comprises an amorphousferromagnetic material. Optionally, the amorphous ferromagnetic materialhas a thickness of less than 30 microns. Typically, the amorphousferromagnetic material is sandwiched between two polymer layers.Preferably, the magnetic flux guide comprises a plurality of layers ofamorphous ferromagnetic material separated by electrically insulatingmaterial.

In some embodiments, the magnetic flux guide comprises a wafer of theamorphous ferromagnetic material. Preferably, the wafer is at leastpartially split so as to reduce the build up of eddy currents.Optionally, the wafer is circular and having a split extending along atleast one diameter. In certain embodiments, the wafer is cut from asheet of the amorphous ferromagnetic material. Alternatively, themagnetic flux guide comprises microwires of the amorphous ferromagneticmaterial. Optionally, the microwires form a cloth.

It is a particular aim of the invention to present an inductive powertransfer system comprising at least one inductive power outlet fortransferring power inductively to at least one inductive power receiver,the inductive power outlet comprising at least one primary inductorwired to a power source via a driver, and the inductive power receivercomprising at least one secondary inductor for coupling with the primaryinductor, the secondary inductor for providing power to an electricload; the inductive power transfer system comprising at least one of theoptimization components selected from the group comprising:

-   -   a low heat-loss full wave rectifier comprising at least one        electronic switch configured to be in its ON state when the        current flowing through the cathode of the switch exceeds a        predetermined threshold;    -   a driver connected between the power source and the primary        inductor, the driver being is configured to provide a driving        voltage across the primary inductive coil, the driving voltage        oscillating at a transmission frequency significantly different        from the resonant frequency of the inductive couple formed by        the primary inductor and the secondary inductor;    -   an inductive power adaptor comprising a grip for handling the        power receiver, the grip being thermally isolated from the power        receiver such that when the power receiver is in operation a        user may handle the adapter without injury;    -   a transmission-guard for preventing the inductive power outlet        from transmitting power in the absence of an electric load        inductively coupled thereto, the transmission-guard comprising        at least one transmission-lock for preventing the primary coil        from connecting to the power supply in the absence of a        transmission-key, and    -   a magnetic flux guide for directing magnetic flux from the        primary inductor to the secondary inductor wherein the magnetic        flux guide comprises an amorphous ferromagnetic material.

In further embodiments the inductive power transfer system comprises atleast two of the optimization components listed above. Preferably, theinductive power transfer system comprises at least three of theoptimization components.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how it may becarried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention; the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawings:

FIG. 1a is a schematic diagram representing an inductive power transfersystem according to an exemplary embodiment of the present invention;

FIG. 1b is a schematic diagram representing an inductive power receiverfor use in the inductive power transfer system of FIG. 1 a;

FIG. 1c is a block diagram representation of the main components of theinductive power transfer system according to the exemplary embodiment ofthe present invention;

FIG. 2a is a block diagram representing the main components of atransmission-guard for an inductive power outlet according to anotherembodiment of the present invention;

FIG. 2b is a schematic representation of an inductive power outletprotected by an exemplary transmission-guard according to a furtherembodiment of the present invention wherein a transmission-lock isreleased by a magnetic key;

FIGS. 2c-e are schematic representations of a transmission-guardaccording to another embodiment of the invention in which atransmission-lock is releasable by a passive optical transmission-key;

FIG. 2f is a schematic representation of a transmission-guard accordingto a further embodiment of the invention in which a transmission-lock isreleasable by an active optical transmission-key;

FIG. 3a is a circuit diagram of a full-wave diode bridge rectifier ofthe prior art;

FIG. 3b is a diagram of a Power MOSFET of the prior art;

FIG. 4a is a block diagram of a first synchronous full-wave rectifier inwhich two of the diodes of the diode bridge of FIG. 3 have been replacedby electronic switches;

FIG. 4b is a block diagram of a second synchronous full-wave rectifieraccording to an exemplary embodiment of the invention in which all fourdiodes of the diode bridge of FIG. 3 have been replaced by electronicswitches;

FIG. 4c is a schematic diagram showing a current triggered Power MOSFETwhich draws a gate signal from the current flowing through its drainterminal;

FIG. 4d is a graphical representation of the variations in drain-currentand state of the MOSFET of FIG. 4c , over a single cycle of a sinusoidalinput voltage;

FIG. 4e is a circuit diagram representing a synchronous full-wave MOSFETbridge rectifier according to another embodiment of the invention;

FIG. 5a shows schematic diagram of a computer being powered by aninductive power outlet via an inductive power adapter according to afurther embodiment of the present invention;

FIG. 5b is an isometric projection of an inductive power adapteraccording to an exemplary embodiment of the invention;

FIG. 5c is an exploded view showing the internal components of the powerreceiver of the exemplary embodiment;

FIG. 5d is a side view cross section of the power receiver of theexemplary embodiment;

FIG. 5e is an exploded view of an inductive power receiver having amagnetic flux guide according to another embodiment of the invention;

FIG. 5f is an isometric view of the inductive power receiver of FIG. 5e;

FIG. 6a is a block diagram showing the main elements of an inductivepower transfer system with a feedback signal path;

FIG. 6b is a graph showing how the amplitude of operational voltagevaries according to frequency;

FIG. 6c is a schematic diagram representing a laptop computer drawingpower from an inductive power outlet;

FIG. 6d is a flowchart showing a method for regulating power transfer byvarying the power transmission frequency in an inductive power transfersystem;

FIG. 6e is a circuit diagram of an inductive power transfer systemincluding a peak detector for detecting large increases in transmissionvoltage;

FIG. 7a is a block diagram showing the main elements of an inductivepower transfer system with an inductive feedback channel according toanother embodiment of the present invention;

FIG. 7b is a graph showing how the amplitude of operational voltage ofan inductive power transfer system varies according to the voltagetransmission frequency and the resonant frequency of the system;

FIG. 7c is a circuit diagram of an inductive power transfer systemincluding an inductive feedback channel for providing coil-to-coilsignal transfer concurrently with uninterrupted inductive power transferbetween the coils in accordance with another embodiment of theinvention, and

FIG. 7d is a flowchart showing a method for transferring a signal fromthe secondary inductive coil to a primary inductive coil of an inductivepower transfer system according to still a further embodiment of theinvention.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Reference is now made to FIGS. 1a and 1b showing an inductive poweroutlet 200 and an inductive power receiver 300 for use in an exemplaryinductive power transfer system 100 according to an exemplary embodimentof the invention.

The inductive power outlet 200 consists of four primary inductors 220a-d incorporated within a platform 202. The inductive power receiver 300includes a secondary inductor 320 incorporated within a case 302 foraccommodating a mobile telephone 342. When a mobile telephone 342 isplaced within the case 302 a power connector 304 electrically connectsthe secondary inductor 320 with the mobile telephone 342. As shown inFIG. 1a , the inductive power receiver 300 may be placed upon theplatform 202 in alignment with one of the primary inductors 220 b sothat the secondary inductor 320 inductively couples with the primaryinductor 220 b.

Referring now to FIG. 1c , which shows a block diagram representing themain components of the inductive transfer system 100, various featuresare included to improve power transfer across the inductive couple.

The inductive power outlet 200 includes a primary inductor 220, wired toa power supply 240 via a driver 230. The driver 230 typically includeselectronic components, such as a switching unit for example, forproviding an oscillating electrical potential to the primary inductor220. The oscillating electrical potential across the primary inductor220 produces an oscillating magnetic field in its vicinity.

The inductive power receiver 300 includes a secondary inductor 320 wiredto an electric load 340, typically via a rectifier 330. The secondaryinductor 320 is configured such that, when placed in the oscillatingmagnetic field of an active primary inductor 220, a secondary voltage isinduced across the secondary inductor 320. The secondary voltage may beused to power the electric load 340. It is noted that an inducedsecondary voltage across the secondary inductor 320 produces analternating current (AC). Where the electric load 340 requires directcurrent (DC), such as for charging electrochemical cells, the rectifier330 is provided to convert AC to DC.

In contradistinction to prior art inductive power transfer systems,which have proved impractical or commercially unviable, embodiments ofthe current invention include further elements for improving theefficiency of power transfer from the inductive power outlet 200 to theinductive power receiver 300. For example, preferred embodiments of theinvention include a signal transfer system 400, an alignment mechanism500 and a magnetic flux guide 600.

The signal transfer system 400 provides a channel for passing signalsbetween the inductive power receiver 300 and the inductive power outlet200. The signal transfer system 400 includes a signal emitter 420,associated with the inductive power receiver 300 and a signal detector440, associated with the inductive power outlet 200. Signals may performa variety of functions such as inter alia, confirming the presence of apower receiver 300, regulating power transfer or for communicatingrequired power transmission parameters. The latter being particularlyuseful in systems adapted to work at multiple power levels. Varioussignal transfer systems may be used such as optical, inductive,ultrasonic signal emitters or the like in combination with appropriatedetectors.

The alignment mechanism 500 is provided to facilitate the alignment ofthe secondary inductor 320 with the primary inductor 220 therebyimproving the efficiency of the inductive transfer system 100. Where theuser is able to see the primary inductor 220 directly, the secondaryinductor 320 may be aligned by direct visual observation. However, wherethe primary inductor 220 is concealed behind an opaque surface,alternative alignment mechanisms 500 may be necessary. Such alignmentmechanisms 500 may include tactile, visual and/or audible indications,for example.

The magnetic flux guide 600 is provided to guide magnetic flux from theprimary inductor 220 to the secondary inductor 320 and to prevent fluxleakage out of the inductive power transfer system 100, particularlyinto metallic or other conductive materials in the vicinity.

Prior art inductive power transfer systems have typically been eitherinefficient or impractical for powering electrical devices wirelessly.As a result, in spite of the long felt need to reduce trailing wires,the use of inductive power transfer has been generally limited to lowpower applications such as the charging of batteries. In order to bepractical, an inductive power transfer system must be efficient, safeand unobtrusive, preferably having small dimensions and beinglightweight. As will be described herein below, embodiments of thepresent invention are directed towards providing an inductive powertransfer system which answers these requirements.

Particular aspects of the current invention include:

-   -   A transmission-guard for preventing the inductive power outlet        200 from transmitting power in the absence of an inductive power        receiver 300.    -   An AC-DC rectifier 330 which uses electronic switches for        reducing heat loss from diodes.    -   An inductive power receiver 300 having a heat dissipation system        such that a user may comfortably and safely handle the inductive        power receiver 300.    -   A magnetic flux guide 600 constructed from thin materials and        which is adapted to improve flux linkage between the primary        inductor 220 and the secondary inductor 320 as well as to        prevent flux leakage into the surroundings.    -   A driver 230 configured and operable to generate a driving        voltage which oscillates at a transmission frequency which is        substantially different from the resonant frequency of the        inductive couple.

Any one of the above described aspects by itself represents asignificant improvement to the prior art. However, it is particularlynoted that for any inductive power transfer system 100 to be practicalfor powering electrical devices, it needs to incorporate at least two ormore of the above described features in combination. More detaileddescriptions of embodiments of the invention which incorporate thesefeatures are given below.

Transmission-Guard

Reference is now made to FIG. 2a which shows a block diagramrepresenting a transmission-guard 2100 for preventing an inductive poweroutlet 2200 from transmitting power in the absence of a secondary unit2300 connected to an electric load 2340, according to another embodimentof the invention.

The inductive power outlet 2200 consists of a primary coil 2220, wiredto a power supply 2240, for inductively coupling with a secondary coil2320 wired to an electric load 2340. The primary coil 2220 is wired tothe power supply 2240 via a driver 2230 which provides the electronicsnecessary to drive the primary coil 2220. Driving electronics mayinclude a switching unit providing a high frequency oscillating voltagesupply, for example. Where the power outlet 2200 consists of more thanone primary coil 2220, the driver 2230 may additionally consist of aselector for selecting which primary coil 2220 is to be driven.

It is a particular feature of this embodiment of the invention that atransmission-guard 2100 is provided consisting of a transmission-lock2120 connected in series between the power supply 2240 and the primarycoil 2220. The transmission-lock 2120 is configured to prevent theprimary coil 2220 from connecting to the power supply 2240 unless it isreleased by a transmission-key 2140. The transmission-key 2140 isassociated with the secondary unit 2300 and serves to indicate that thesecondary coil 2320 is aligned to the primary coil 2220.

With reference to FIG. 2b , a schematic representation is shown of aninductive power outlet 2200 protected by an exemplary magnetictransmission-guard 2100 according to another embodiment of the presentinvention. Power may only be provided by the protected power outlet 2200when an authenticated secondary unit 2300 is aligned thereto.

The protected power outlet 2200 includes a magnetic transmission-lock2120 consisting of an array of magnetic switches 2122 electricallyconnected in series between the primary coil 2220 and the driver 2230. Amagnetic transmission-key 2140 consisting of an array of magneticelements 2142 is provided within the authenticated secondary unit 2300.

The configuration of magnetic elements 2142 in the transmission-key 2140is selected to match the configuration of magnetic switches 2122 in thetransmission-lock 2120. The authenticated secondary unit 2300 may bealigned with the protected induction outlet 2200 by aligning both thetransmission-key 2140 with the transmission-lock 2120 and the secondarycoil 2320 with the primary coil 2220. Once correctly aligned, all themagnetic switches 2122 in the transmission-lock 2120 are closed and thedriver 2230 is thereby connected to the primary coil 2220.

Various examples of magnetic switches 2122 are known in the artincluding for example reed switches, Hall-effect sensors or such like.Such magnetic switches 2122 may be sensitive to any magnetic elements2142 such as either North or South poles of permanent magnets orelectromagnetic coils for example. It is further noted that Hall-effectsensors may be configured to sense magnetic fields of predeterminedstrength.

According to certain embodiments, the magnetic transmission-key 2140 mayconsist of a permanent magnet and a ferromagnetic element incorporatedwith in the secondary unit 2300. The characteristics of the magneticfield produced by a transmission-key of this type depend upon thestrength and position of the permanent magnetic as well as thedimensions and characteristics of the ferromagnetic element. Themagnetic transmission-lock 2120 may consist of an array of magneticswitches, such as unipolar Hall switches for example, which arestrategically placed and orientated such that they connect the primarycoil 2220 to the driver 2230 only when triggered by a particularcombination of a permanent magnet and ferromagnetic element.

It is noted that permanent magnets may commonly be provided to assistwith alignment of the secondary coil 2320 to the primary coil 2220.Ferromagnetic elements may also be commonly included in secondary units2300 for providing flux guidance from the primary coil 2220 to thesecondary coil 2320. The magnetic transmission-lock 2120 may thereforebe made sensitive to these components. Indeed a single magnetictransmission-lock 2120 may be provided which is configured to detectvarious secondary units and to selectively connect more than one primarycoil 2220 depending on the secondary unit detected.

Referring back to FIG. 2a , according to other embodiments of thetransmission-guard 2100, a power outlet 2200 may be protected by atransmission-lock 2120 which may be released when a release signal S_(R)is received by a detector 2124. The release signal S_(R) may be activelyemitted by the transmission-key 2140 or alternatively thetransmission-key may passively direct the release signal towards thedetector 2124.

One example of a passive transmission-key 2140 is shown in FIGS. 2c-ewhich represent an optical transmission-guard 2100 according to afurther embodiment of the invention.

The transmission-guard 2100 consists of an active opticaltransmission-lock 2120′ incorporated within an inductive power outlet2200′ and a passive optical transmission-key 2140′ incorporated withinthe secondary unit 2300.

With particular reference to FIG. 2c , the optical transmission-lock2120′ includes a switch 2122′, an optical detector 2124′, such as aphotodiode, a phototransistor, a light dependent resistor or the like,and an optical emitter 2126′ such as light emitting diode (LED). Theswitch 2122′ is normally open but is configured to close when a releasesignal S_(R) is received by the optical detector 2124′, therebyconnecting a primary coil 2220 to a driver 2230. The optical emitter2126′ is configured to emit the optical release-signal S_(R) which isnot directly detectable by the optical detector 2124′.

Referring now to FIG. 2d , the optical transmission-key 2140′ includes abridging element 2142′ such as an optical wave-guide, optical fiber,reflector or the like. The bridging element 2142′ is configured todirect the optical release-signal S_(R) from the optical emitter 2124′towards the optical detector 2126′, when a secondary coil 2320 isaligned with the primary coil 2220.

When the secondary unit 2300 is correctly aligned with the inductivepower outlet 2200, as shown in FIG. 2e , the secondary coil 2320 alignswith the primary coil 2220′ and the passive optical transmission-key2140′ aligns with the optical transmission-lock 2120′. The opticalrelease-signal S_(R) is thus detected by the optical detector 2126′ andthe switch 2122′ is closed connecting the primary coil 2220 to thedriver 2230.

It is noted that many materials are partially translucent to infra-redlight. It has been found that relatively low intensity infra red signalsfrom LEDs and the like, penetrate several hundred microns of commonmaterials such as plastic, cardboard, Formica or paper sheet, to asufficient degree that an optical detector 2124′, such as a photodiode,a phototransistor, a light dependent resistor or the like, behind asheet of from 0.1 mm to 2 mm of such materials, can receive and processthe signal. For example a signal from an Avago HSDL-4420 LEDtransmitting at 850 nm over 24 degrees, may be detected by an EverlightPD 15-22C-TR8 NPN photodiode, from behind a 0.8 mm Formica sheet. Forsignaling purposes, a high degree of attenuation may be tolerated, andpenetration of only a small fraction, say 0.1% of the transmitted signalintensity may be sufficient.

Although an optical transmission-key 2140′ is described above, it willbe appreciated that other passive transmission-keys may incorporatebridging elements configured to guide release-signals of other types.For example, a ferromagnetic bridge may be incorporated for transmittingmagnetic release-signal from a magnetic element to a magnetic detectorsuch as a Hall-effect sensor or the like. The magnetic emitter in such acase may be the primary coil itself.

Alternatively, audio signals may be guided through dense elements, orlow power microwaves along microwave wave guides for example.

An example of an active optical transmission-key 2140″ is shown in FIG.2f representing a transmission-guard 2100″ according to anotherembodiment of the invention.

The transmission-guard 2100″ of this embodiment includes atransmission-lock 2120″ incorporated within an inductive power outlet2200 and an active optical transmission-key 2140″ incorporated withinsecondary unit 2300.

The active optical transmission-key 2140″ includes an optical emitter2142″, configured to emit an optical release-signal S_(R), and thetransmission-lock 2120″ includes a switch 2122″ and an optical detector2124″. The transmission-lock 2120″ is configured to close the switch2122″ thereby connecting a primary coil 2220 to a driver 2230 when theoptical detector 2124″ receives the release-signal S_(R).

When the secondary unit 2300 is aligned with the inductive power outlet2200, the transmission-key 2140″ emits an optical release-signal S_(R)which is received by the optical detector 2124″ of the transmission-lock2120″ and this closes the switch 2122″. Thus the inductive power outlet2200″ is enabled to transfer power to the secondary coil 2320.

It will be appreciated that a release signal S_(R) may be coded toprovide a unique identifier. Coding may be by modulation of frequency,pulse frequency, amplitude or the like. The code may be used, forexample, to identify the type or identity of the secondary unit forauthentication. Other data may additionally be encoded into therelease-signal. This data may include required power transmissionparameters, billing information or other information associated with theuse of the power outlet.

Although an optical active transmission-key 2140″ is described above, itwill be appreciated that other active transmission-keys may emit othertypes of release-signals. For example, the secondary coil 2320 may beused to transmit a magnetic release-signal to a magnetic detectorincorporated in the transmission-lock. This could be a Hall-effectsensor or the like or even the primary coil 2220 itself.

To actively emit a release-signal transmission-keys typically require apower source. In some cases, particularly where the secondary unit isincorporated into a portable electrical device, power may be provided byinternal power cells with the secondary unit. Alternatively, power maybe drawn from a power pulse transferred from the primary coil to thesecondary coil.

In certain embodiments of the invention, the inductive power outlettransfers a periodic low energy power pulse, for example a pulse of afew milliseconds duration may be transmitted by the primary coil at afrequency of 1 hertz or so. When a secondary coil is brought into thevicinity of the primary coil the power may be transferred to thesecondary coil and may be used to power an active transmission-key.

In other embodiments of the transmission-guard, a firsttransmission-lock (preferably a passive transmission-lock) associatedwith the secondary unit, releases a first transmission-lock therebyindicating the probable presence of a secondary coil. A low energy powerpulse is then emitted by the primary coil to power an active secondtransmission-key which may release a second transmission-lock therebyconnecting the primary coil to a driver.

Synchronous Rectifier

Reference is now made to FIG. 3a showing a circuit diagram of a typicalfull-wave rectifier 3100 of the prior art. The rectifier has two inputterminals T₁ and T₂ and two output terminals T₃ and T₄. When analternating current source AC_(in) is wired to the two input terminalsT₁ and T₂, a direct current output DC_(out) may be drawn from the twooutput terminals T₃ and T₄ of the rectifier 3100.

Four diodes D₁₋₄ are arranged so that two diodes D₁ and D₂ form a firstbranch 3110 of a Graetz circuit and the other two diodes D₃ and D₄ forma second branch 3120 of the Graetz circuit. The anodes of two upstreamdiodes D₁ and D₃ are wired to the first output terminal T₃ and thecathodes of the two downstream diodes D₂ and D₄ are wired to the secondoutput terminal T₄. The cathode of the first upstream diode D₁ and theanode of first downstream diode D₂ are wired to the first input terminalT₁ and the cathode of the second upstream diode D₃ and the anode ofsecond downstream diode D₄ are wired to the second input terminal T₂.

When the polarity of the first input terminal T₁ is positive relative tothe second input terminal T₂, current flows through the first downstreamdiode D₂ and through the second upstream diode D₃. When the polarity ofthe first input terminal T₁ is negative relative to the second inputterminal T₂, current flows through the second downstream diode D₄ andthrough the first upstream diode D₁.

Diode bridge rectifiers, such as that shown in FIG. 3a , are used toproduce an output with a fixed polarity that is independent of thepolarity of the input. Such diode bridge rectifiers may be used inAC-to-DC power converters, for example. Optionally, the output issmoothed by a smoothing capacitor C.

It will be appreciated that power is lost from each diode with eachreversal of polarity. In high frequency power converters, where thepolarity of the input terminals T₁ and T₂ may oscillate at a frequenciesof 100 kHz or more, such power losses may result in significant heatingof the bridge circuit and its surrounding components, which may resultin reduced reliability or failure.

Power loss may be reduced by replacing diodes with electronic switches,such as the Power MOSFETs shown in FIG. 3a , which have much lowerassociated power loss. FIG. 4a is a block diagram of one suchsynchronous full-wave rectifier 4200 in which the first downstream diodeD₂ and the second downstream diode D₄ of the diode bridge of FIG. 3ahave been replaced by two electronic switches M₂ and M₄.

The electronic switches M₂ and M₄ are controlled by switching signals G₂and G₄ which switch them between the ON and OFF states. The switchingsignal G₂ controlling the electronic switch M₂ must be synchronized toswitch to the ON state whenever the polarity of the first input terminalT₁ is positive relative to the second input terminal T₂. The switchingsignal G₄ controlling the electronic switch M₄ must be synchronized toswitch to the ON state whenever polarity of the first input terminal T₁is negative relative to the second input terminal T₂.

Typically, this synchronization is achieved by drawing the firstswitching signal G₂ from the voltage of the second input terminal T₂ anddrawing the second switching signal G₄ from the voltage of the firstinput terminal T₁.

The above described synchronous full-wave rectifier 4200 in which twodiodes are replaced by MOSFETs may reduce power loss from the rectifierby up to 50% as compared with the diode bridge rectifier 4100 of theprior art. Where further reduction in power loss is required it would bedesirable to replace the remaining two diodes D₁ and D₃ with electronicswitches. However, it is much more difficult to synchronize fourelectronic switches without inadvertently causing short circuits betweeneither the input or output terminals.

FIG. 4b is a block diagram of a second synchronous full-wave rectifier4300 in which all four diodes D₁₋₄ of the diode bridge of FIG. 3a havebeen replaced by electronic switches M₁₋₄. In order to provide an outputDC_(out) of constant polarity, the switching signals G₁₋₄ need to becarefully controlled.

When the polarity of the first input terminal T₁ is positive relative tothe polarity of the second input T₂, the first upstream and seconddownstream electronic switches M₁ and M₄ must be switched to the OFFstate and the first downstream and second upstream electronic switchesM₂ and M₃ must be switched to the ON state. When the polarity of thefirst input terminal T₁ is negative relative to the polarity of thesecond input terminal T₂, the first upstream and second downstreamelectronic switches M₁ and M₄ must be switched to the ON state and theelectronic switches first downstream and second upstream electronic M₂and M₃ must be switched to the OFF state.

Synchronization of the switching signals G₁₋₄, is complicated by anadditional constraint. In order to prevent shorting across the outputterminals, the upstream and downstream electronic switches along acommon branch 4310, 4320 must never be in the ON state at the same time.In practice, when both of the switching signals G₁ and G₂ controllingthe two electronic switches M₁ and M₂ along the first branch 4310 areeach drawn from one of the input terminals T₁ and T₂, the two switchesM₁ and M₂ are periodically both in their ON states. Because the switchesM₁ and M₂ are adjacent along the first branch 4310 of the circuit, ashort circuit is formed between the output terminals T₃ and T₄. Similarshorting may occur along the second branch 4320 when the switchingsignals G₃ and G₄ which control the other two electronic switches M₃ andM₄ are each drawn from one of the input terminals T₁ and T₂.

According to preferred embodiments of the invention, only the switchingsignals G₂ and G₄ for the downstream electronic switches M₂ and M₄ aredrawn directly from the voltage at the input terminals T₁ and T₂ whilstthe switching signals G₁ and G₃ for the upstream switches M₁ and M₃ arecontrolled independently. Preferably, the switching signals G₁ and G₃are responsive to changes in the cathode current of switches M₁ and M₃respectively.

FIG. 4c shows an exemplary current-triggered synchro-rectifier 4330,which may serve as an electronic switch M incorporated into a bridgesynchro-rectifier 4300. The current-triggered synchro-rectifier 4330includes a Power MOSFET 4130, such as that shown in FIG. 3b , and acurrent monitor 4332. The current monitor 4332 is wired to the drainterminal 4136 of the Power MOSFET 4130 and is configured to send acurrent-based gate signal G_(i) to the gate terminal 4138 of the PowerMOSFET when the drain-current I_(d) exceeds a predetermined thresholdI_(th). Although in the above example the current-triggeredsynchro-rectifier 4330 includes an n-channel MOSFET 4130, it will beappreciated that in other embodiments current-triggeredsynchro-rectifiers may incorporate p-channel MOSFETs.

In order to understand the functioning of the current-triggeredsynchro-rectifier 4330 consider the case where a sinusoidal alternatingvoltage is connected across the cathode 4334 and the anode 4336terminals of the current-triggered synchro-rectifier 4330. FIG. 4d showsthree graphs showing variations in 1) the voltage drop V_(d) from thecathode 4334 to the anode 4336, 2) the drain-current I_(d), and 3) theMOSFET state during one voltage cycle.

For the first half of the sinusoidal cycle the voltage drop V_(d)between the cathode 4334 and the anode 4336 is negative, thus thepolarity of the cathode 4334 is negative relative to the anode 4336.Consequently, no current flows through the drain-terminal 4136 and theMOSFET remains in the OFF state.

At the beginning of the second half of the sinusoidal cycle, the voltagedrop V_(d) between the cathode 4334 and the anode 4336 increases abovezero. The polarity of the cathode 4334 becomes positive relative to theanode. 4336 so a small drain-current I_(d) begins to flow through thediode 4132. This current is measured by the current monitor 4332.

During the third quarter of the cycle, the voltage drop V_(d) betweenthe cathode 4334 and the anode 4336 continues to rise. The currentmonitor 4332 measures an increasing drain-current I_(d).

When the drain-current I_(d) exceeds the predetermined threshold I_(th),the current-based gate signal G_(i) triggers the MOSFET 4130 to switchto the ON state.

As long as the MOSFET 4130 is in the ON state, current flows through theohmic conductive path of the electronic switch 4131. Consequently, thedrain-current I_(d) varies in proportion to the voltage drop V_(d).

During the last quarter of the cycle, the voltage drop V_(d) between thecathode 4334 and the anode 4336 decreases. The current monitor 4332measures a decreasing drain-current I_(d).

When the drain-current falls below the predetermined threshold I_(th),the current-based gate signal G_(i) triggers the MOSFET 4130 to switchto the OFF state.

FIG. 4e is a circuit diagram representing a synchronous full-wave bridgerectifier 4400 incorporated within an inductive power receiver accordingto a further embodiment of the invention. The electronic switches M₁₋₄are all MOSFET transformers having three terminals: a source terminal, adrain terminal and a gate terminal. The upstream MOSFETs M₁ and M₃ areboth n-channel MOSFETs and their source terminals are both wired to thefirst output terminal T₃ of the rectifier. The downstream MOSFETs M₂ andM₄ are both p-channel MOSFETs and their source terminals are both wiredto the second output terminal T₄ of the rectifier. The drain terminalsof the first upstream MOSFET M₁ and the first downstream MOSFET M₂ areboth wired to the first input terminal T₁ of the rectifier and the drainterminals of the second upstream MOSFET M₃ and the second downstreamMOSFET M₄ are both wired to the second input terminal T₃ of therectifier.

The input terminals T₁ and T₂ are wired to a secondary coil L₂ of apower transformer which is inductively coupled to a primary coil (notshown). The secondary coil L₂ provides an alternating current input tothe two input terminals T₁ and T₂.

The gate terminals of the downstream MOSFETs M₂ and M₄ are wired to theinput terminals T₂ and T₁ via smoothing circuits 4420, 4440respectively. The switching signals G₂ and G₄, are therefore in out ofphase with each other.

The gate terminals of the upstream MOSFETs M₁ and M₃ receive switchingsignals G₁ and G₃ driven by their own drain-currents I_(d1) and I_(d3).The drain current I_(d1) of the first upstream MOSFET M₁ is monitored bya first current transformer 4410, in which a primary current monitorcoil CT_(1P) transfers the current signal to a secondary current monitorCT_(2S) the output of which is rectified and relayed to a first inputIN₁ of a driver 4450 which amplifies the signal before outputting asignal from a first output OUT₁. This first output signal from thedriver is then fed back to the first upstream MOSFET M₁ such that whenthe drain current I_(d1) exceeds a threshold value the MOSFET M₁switches itself to the ON state. This produces a switching signal G₁ atthe same frequency as the alternating current input AC_(in).

Similarly the drain current I_(d3) of the second upstream MOSFET M₂ ismonitored by a second current transformer 4430, in which a primarycurrent monitor coil CT_(2P) transfers the current signal to a secondarycurrent monitor CT_(2S) the output of which is rectified and relayed toa second input IN₂ of the driver 4450 which amplifies the signal beforeoutputting a signal from a second output OUT₂. The second output signalfrom the driver is then fed back to the second upstream MOSFET M₃ suchthat when the drain current I_(d2) exceeds a threshold value the MOSFETM₃ switches itself to the ON state. This produces a switching signal G₃at the same frequency as the alternating current input AC_(in).

Although in the example here above, current transformers 4410, 4430 areused to monitor the drain-currents I_(d1), I_(d2), in alternativeembodiments other current monitors such as ammeters, galvanometers, Halleffect sensors or the like may be preferred.

Heat Dissipation within Inductive Power Receivers

Reference is now made to FIG. 5a showing a laptop computer 5300 drawingpower from an inductive power outlet 5200 via an inductive power adapter5100, according to a further embodiment of the present invention. Theadaptor is configured such that it can be safely handled by a user whileit is operation.

The power adapter 5100 includes an inductive receiver 5120, housed in acasing 5160 and a power connector 5140 for connecting to an electricaldevice, such as the computer 5300. The inductive receiver 5120 includesa secondary inductor 5122 configured to couple with a primary inductor5220 in the power outlet 5200. Typically, the primary inductor 5220 iswired to a power source 5240 via a driver 5230. The driver 5230 providesan oscillating driving voltage to the primary inductive coil 5220.

Preferably, an alignment mechanism (not shown) is provided for aligningthe secondary inductor 5122 to the primary core 5220. The alignmentmechanism may consist of a primary magnetic element in the inductiveoutlet configured to snag and/or engage a secondary magnetic element inthe power adaptor 5100.

It will be appreciated that electrical components of power convertersgenerate heat. There are a number of problems associated with the heatgenerated in an inductive receiver 5120, particularly in systems runningat high power above say 50 W or 100 W. Heat produces high temperatureswhich can reduce overall efficiency and may also reduce the reliabilityof components. Much design effort is typically required to overcome thisproblem, and other factors such as the dimensions of the system may becompromised as a result.

In practice, electrical components of the power adapter 5100 areselected which function at high temperatures. However, the maximumtemperature of the casing 5160 is further constrained by the requirementthat it is to be handled by the user. If the casing 5160 reaches hightemperatures, above 50 degrees Celsius or so, a user may find handlingthe adapter to be unpleasant and may even be at risk of injury. In orderto allow a user to comfortably and safely handle the adaptor 5100, it isa particular feature of the present invention that a heat dissipationsystem for directing heat away from the hand grip 5162.

The heat dissipation system may be better understood with reference toFIGS. 5b-d showing an exemplary inductive power adapter 5100 accordingto another embodiment of the invention. FIG. 5b shows an isometricprojection, FIG. 5c shows an exploded view and FIG. 5d shows across-section through the same embodiment of the power adaptor 5100.

The exemplary power adapter 5100 includes an inductive receiver 5120,and a heat sink 5130 housed between a lower casing 5160L, and an uppercasing 5160U and a power connector 5140 which can be wound around a handgrip 5162 for storage.

The inductive power receiver 5120 consists of a secondary inductive coil5122 a ferromagnetic disk 5124 and a printed circuit board (PCB) 5126.The heat sink 5130 of the exemplary embodiment consists of a metallicdisk sandwiched between the inductive receiver 5120 and the upper casing5160U. The ferromagnetic disk 5124 may serve as a flux guiding core toimprove inductive coupling between the secondary inductive coil 5122 anda primary inductive coil 5220 (FIG. 1) of an inductive power outlet5200.

When the power adapter 5100 is in operation, heat is generated by anumber of components of the inductive receiver 5120. An alternatingcurrent is induced in the secondary inductive coil 5122 thereforecausing the coil wire to heat up. Furthermore hot spots are typicallygenerated around certain electrical components typically provided on thePCB 5126, such as rectifiers, diodes, MOSFETS, power regulators, LDOs,feedback transmitters or the like.

The heat sink 5130 is typically a thermal conductive material such asaluminum, copper or the like which serves to distribute heat more evenlyaround the inductive receiver 5120. Preferably, thermal vias areprovided through the PCB 5126 and thermal grease or a similar agent isused to improve thermal contact between the heat sink 5130, PCB 5126,ferromagnetic disk 5124 and secondary coil 5122.

Air outlets 5132 are provided in the top 5161 of the upper casing 5160Uallowing hot air from inside the power adaptor to escape into theatmosphere. Air inlets 5134 are provided in the bottom 5165 and sides5167 of the lower casing 5160L and on the sides 5163 of the upper casing5160U allowing cool air to enter into the power adaptor from below. Itis a particular feature of the exemplary embodiment that the outerdiameter d of the heat sink is smaller the inner diameter D of thecasing 5160 thus allowing air to circulate around the inductive receiver5120. Thus hot air heated by the inductive power receiver 5120 flows outof the adapter 5100 through the outlets 5132 and cool air from outsideis drawn into the adapter 5100 through said air inlets 5134. The handgrip 5162 may be additionally protected from heat by a barrier ofthermal insulating material.

It is noted that the air outlets 5132 may allow dust to enter the poweradapter 5100. In some embodiments therefore a dust-guard is provided toprevent dust from entering the outlets 5132. In the exemplaryembodiment, the grip 5162 overhangs the outlets 5132 serving as adust-guard to prevent dust from entering the adapter 5100 whilst inoperation. When not in operation, the power connector 5140 may be woundaround the hand grip 5162, thereby providing further protection againstdust.

In certain embodiments, the PCB 5126 includes a light emitting diode(not shown) used as a feedback transmitter for sending signals to anoptical detector in the power outlet 5200 (FIG. 5a ). It will beappreciated that in such embodiments, it is necessary that a clearline-of-sight is maintained between the optical emitter and detector. Tothis end, in preferred embodiments an optical window, transparent to thewavelength of the wavelength of the optical transmission, is providedthrough the secondary inductive coil 5122, ferrite disk 5124, lowercasing 5160L and other layers between the PCB 5126 and the primary coil5220 (FIG. 5a ).

Magnetic Flux Guidance

Referring now to FIGS. 5e and 5f , an inductive power receiver 5200 isshown including a secondary inductor 5220, a magnetic flux guide 5260and a PCB 5270, according to a further embodiment of the invention. Thesecondary inductor 5220 is configured to receive power inductively froma primary inductor of an inductive power outlet (not shown). Themagnetic flux guide 5260 is provided to direct magnetic flux from theprimary inductor to the secondary inductor 5220 and to reduce fluxleakage to the surroundings. The magnetic flux guide 5260 consists of aferromagnetic core 5262 and a magnetic shield 5264. The ferromagneticcore 5262 is provided to guide magnetic flux from an active primaryinductor to the secondary inductor 5220.

In preferred embodiments, the ferromagnetic core 5262 is constructedfrom amorphous ferromagnetic material, typically cut into wafers from asheet approximately 20 microns thick or so. In one exemplary embodiment,the ferromagnetic core consists of two amorphous ferromagnetic wafers5262 a, 5262 b. A first wafer 5262 a is adhered to the primary inductor5220 by a first adhesive insulating layer 5265 a. A second wafer 5262 bis adhered to the first wafer 5262 a by a second adhesive insulatinglayer 5265 b. The two wafers 5262 a, 5262 b serve as a ferromagneticcore guiding magnetic flux from a primary inductor to the secondaryinductor 5220. It is a particular feature of preferred embodiments thatthe ferromagnetic wafers 5262 a, 5262 b each have a radial slit 5265 a,5265 b to prevent the build up of eddy currents within the wafer due tothe oscillating magnetic field produced by the primary inductor. Wherethe wafer has a circular cross section, the slit may extend inwardlydiametrically from the circumference.

The magnetic shield 5264 is provided to prevent flux leakage into thesurroundings. Preferably, the magnetic shield 5264 is also fabricatedfrom a sheet of thin amorphous ferromagnetic material and may be adheredto the PCB by a third adhesive insulating layer 5265 c.

It will be appreciated that a magnetic shield is of particularimportance when the inductive receiver 5200 is mounted upon a conductivesurface or a device containing conductive components. Thus, for example,when such an inductive power receiver 5200 is mounted upon an electricaldevice, such as a computer, mobile telephone or the like, the magneticshield 5264 prevents magnetic flux from leaking into the metalliccomponents of the electrical device and causing them to heat up.

Amorphous ferromagnetic sheets may have a thickness of around 20microns. When laminated by a polymer laminate on both sides the overallthickness of the sheet is around 60 microns. Thus, in contradistinctionto other ferrite elements used to guide magnetic flux in inductivesystems, amorphous ferromagnetic materials may be used to fabricate anextremely thin magnetic guide 5260. A thin magnetic guide 5260 in turnallows the inductive power receiver 5200 to be flexible and unobtrusive.It will be appreciated that these considerations are very important inthe design and manufacture of device mounted inductive receivers.Various methods of fabricating magnetic guiding elements from amorphousferromagnetic material include, inter alia: printing, stamping, cutting,amorphous ferromagnetic microwire cloth and the like.

Power Transmission at a Non-Resonant Frequency

The strength of an induced voltage in the secondary inductor of aninductive couple varies according to the oscillating frequency of theelectrical potential provided to the primary inductor. The inducedvoltage is strongest when the oscillating frequency equals the resonantfrequency of the system. The resonant frequency f_(R) depends upon theinductance L and the capacitance C of the system according to theequation

$f_{R} = {\frac{1}{2\;\pi\sqrt{L\; C}}.}$

Known inductive power transfer systems typically transmit power at theresonant frequency of the inductive coupling. This can be difficult tomaintain as the resonant frequency of the system may fluctuate duringpower transmission, for example in response to changing environmentalconditions or variations in alignment between primary and secondarycoils.

Inductive transfer systems designed to transmit at resonance thereforerequire tuning mechanisms for maintaining transmission at the resonantfrequency of the system. Tuning may be achieved by adjusting the drivingfrequency to seek resonance. For example, U.S. Pat. No. 6,825,620,titled “Inductively coupled ballast circuit” to Kuennen et al. describesa resonance seeking ballast circuit for inductively providing power to aload. The ballast circuit includes an oscillator, a driver, a switchingcircuit, a resonant tank circuit and a current sensing circuit. Thecurrent sensing circuit provides a current feedback signal to theoscillator that is representative of the current in the resonant tankcircuit. The current feedback signal drives the frequency of the ballastcircuit causing the ballast circuit to seek resonance. The ballastcircuit preferably includes a current limit circuit that is inductivelycoupled to the resonant tank circuit. The current limit circuit disablesthe ballast circuit when the current in the ballast circuit exceeds apredetermined threshold or falls outside a predetermined range.

Alternatively, tuning may be achieved by adjusting the characteristicsof the inductive system. For example, U.S. Pat. No. 7,212,414, titled“Adaptive inductive power supply” to Baarman describes a contactlesspower supply which has a dynamically configurable tank circuit poweredby an inverter. The contactless power supply is inductively coupled toone or more loads. The inverter is connected to a DC power source. Whenloads are added or removed from the system, the contactless power supplyis capable of modifying the resonant frequency of the tank circuit, theinverter frequency, the inverter duty cycle or the rail voltage of theDC power source.

Tuning mechanisms such as those described above are necessary in orderto maintain transmission at resonance because resonant transmission ishighly sensitive. At resonance small variations to the system result inlarge changes to the power transferred. A further problem associatedwith resonant transmission is the high transmission voltages involved.At high operating voltages, the capacitors and transistors in thecircuit need to be relatively large.

Reference is now made to FIG. 6a showing a block diagram of the mainelements of an inductive power transfer system 6100 adapted to transmitpower at a non-resonant frequency. The inductive power transfer system6100 consists of an inductive power outlet 6200 configured to providepower to a remote secondary unit 6300 according to another embodiment ofthe invention. The inductive power outlet 6200 includes a primaryinductive coil 6220 wired to a power source 6240 via a driver 6230. Thedriver 6230 is configured to provide an oscillating driving voltage tothe primary inductive coil 6220.

The secondary unit 6300 includes a secondary inductive coil 6320, wiredto an electric load 6340, which is inductively coupled to the primaryinductive coil 6220. The electric load 6340 draws power from the powersource 6240. A communication channel 6120 may be provided between atransmitter 6122 associated with the secondary unit 6300 and a receiver6124 associated with the inductive power outlet 6200. The communicationchannel 6120 may provide feedback signals S and the like to the driver6230.

In some embodiments, a voltage peak detector 6140 is provided to detectlarge increases in the transmission voltage. As will be descried belowthe peak detector 6140 may be used to detect the removal of thesecondary unit 6200, the introduction of power drains, short circuits orthe like.

FIG. 6b is a graph showing how the amplitude of the operational voltagevaries according to the transmission frequency. It is noted that thevoltage is at its highest when the transmission frequency is equal tothe resonant frequency f_(R) of the system, this maximum amplitude isknown as the resonance peak 2. It is further noted that the slope of thegraph is steepest in the regions 4 a, 4 b to either side of theresonance peak 2. Thus in inductive transfer systems, which operate ator around resonance, a small variation in frequency results in a largechange in induced voltage. Similarly, a small change in the resonantfrequency of the system results in a large change in the inducedvoltage. For this reason prior art inductive transfer systems aretypically very sensitive to small fluctuations in environmentalconditions or variations in alignment between the induction coils.

It is a particular feature of embodiments of the current invention thatthe driver 6230 (FIG. 6a ) is configured and operable to transmit adriving voltage which oscillates at a transmission frequency which issubstantially different from the resonant frequency of the inductivecouple. Preferably the transmission frequency is selected to lie withinone of the near-linear regions 6, 8 where the slope of thefrequency-amplitude graph is less steep.

One advantage of this embodiment of the present invention may bedemonstrated with reference now to FIG. 6c . A schematic diagram isshown representing a laptop computer 6340 drawing power from aninductive power outlet 6200 via a secondary power receiving unit 6300.The power receiving unit 6300 includes a secondary inductive coil 6320which is aligned to a primary inductive coil 6220 in the inductive poweroutlet 6200. Any lateral displacement of the secondary power receivingunit 6300 changes the alignment between the secondary inductive coil6320 to the primary inductive coil 6220. As a result of the changingalignment, the combined inductance of the coil pair changes which inturn changes the resonant frequency of the system.

If the inductive power outlet 6200 transmits power at the resonantfrequency of the system, even a small lateral movement would reducesignificantly the amplitude of the induced voltage. Incontradistinction, according to embodiments of the present invention,the inductive power outlet 6200 transmits power at a frequency in one ofthe regions 6, 8 to either side of the resonance peak 2 (FIG. 6b ) wherethe slope of the resonance graph is much shallower. Consequently, thesystem has a much larger tolerance of variations such as lateralmovement.

Another advantage of non-resonant transmission is that the transmissionfrequency may be used to regulate power transfer. In known inductivepower transfer systems, power is typically regulated by altering theduty cycle of the transmission voltage provided by the driver. Thus, itwill be appreciated that when the transmission frequency is not equal tothe resonance frequency of the system, the driver 6230 may be configuredto adjust the transmission frequency in order to regulate the powertransfer.

Referring back to FIG. 6b , the frequency of transmission is selected tobe in the approximately linear region 8 of the curve between a lowerfrequency value of f_(L) and an upper frequency value of f_(U). Atransmission frequency f_(t), higher than the resonant frequency f_(R)of the system, produces an induced voltage of V_(t). The induced voltagecan be increased by reducing the transmission frequency and can bereduced by increasing the transmission frequency. For example, anincrease in transmission frequency of δf produces a decrease in inducedvoltage of δV.

In some embodiments, a communication channel 6120 (FIG. 6a ) is providedbetween the secondary unit 6300 and the inductive power outlet 6200.Such a communication channel 6120, may be used to communicate requiredoperating parameters which, for example, may indicate the transmissionfrequency required by the electric load 6340 to the driver 6230.

Various transmitters 6122 and receivers 6124 may be used with thecommunication channel 6120. Where, as is often the case for inductivesystems, the primary and secondary coils 6220, 6320 are galvanicallyisolated for example, optocouplers may have a light emitting diodeserving as a transmitter which sends encoded optical signals over shortdistances to a photo-transistor which serves as a receiver. Optocouplerstypically need to be aligned such that there is a line-of-sight betweentransmitter and receiver. In systems where alignment between thetransmitter and receiver may be difficult to achieve, optocoupling maybe inappropriate and alternative systems may be preferred such asultrasonic signals transmitted by piezoelectric elements or radiosignals such as Bluetooth, WiFi and the like. Alternatively the primaryand secondary coils 6220, 6320 may themselves serve as the transmitter6122 and receiver 6124.

In certain embodiments, an optical transmitter, such as a light emittingdiode (LED) for example, is incorporated within the secondary unit 6300and is configured and operable to transmit electromagnetic radiation ofa type and intensity capable of penetrating the casings of both thesecondary unit 6300, and the power outlet 6200. An optical receiver,such as a photodiode, a phototransistor, a light dependent resistors ofthe like, is incorporated within the power outlet 6200 for receiving theelectromagnetic radiation.

The communication channel 6120 may further provide a feedback signalduring power transmission. The feedback transmission may communicaterequired or monitored operating parameters of the electric load 6240such as:

-   -   required operating voltage, current, temperature or power for        the electric load 6240,    -   the measured voltage, current, temperature or power supplied to        the electric load 6240 during operation,    -   the measured voltage, current, temperature or power received by        the electric load 6240 during operation and the like.

In some embodiments, a microcontroller in the driver 6230 may use suchfeedback parameters to calculate the required transmission frequency andto adjust the driver accordingly. Alternatively, simple feedback signalsmay be provided indicating whether more or less power is required.

One example of a power regulation method using simple feedback signalsis shown in the flowchart of FIG. 6d . The method involves the followingsteps:

-   -   (a) The driver 6230 provides an oscillating voltage at a        transmission frequency f_(t) which is higher than the resonant        frequency f_(R) of the system.    -   (b) A secondary voltage is induced in the secondary coil 6320.    -   (c) A power monitor in the secondary unit 6300, monitors the        power received by the electric load 6340.    -   (d) If the power received by the electric load 6340 lies within        a predetermined range then no action is taken. If the power        received by the electric load E340 is below the predetermined        range, then a feedback signal of a first type S_(a) is sent to        the driver. If the power received by the electric load 6340 is        above the predetermined range, then a feedback signal of a        second type S_(b) is sent to the driver.    -   (e) A feedback signal is received by the driver 6230.    -   (f) If the received feedback signal is of the first type S_(a),        then the transmission frequency is increased by an incremental        value +δf₁. If the received feedback signal is of the second        type S_(b), then the transmission frequency is decreased by an        incremental value −δf₂.

It is noted that by using the power regulation method described above,when the power received by the load is too high, a series of feedbacksignals of the first type S_(a) will be transmitted until the power isreduced into the acceptable range. Likewise when the power received bythe load is too low, a series of feedback signals of the second typeS_(b) will be transmitted until the power is increased into theacceptable range. It is noted that the positive incremental value δf₁may be greater than, less than or equal to the negative incrementalvalue δf₂.

Alternatively, other power regulation methods using frequency adjustmentmay be used. For example, in alternative embodiments, the operatingparameters of the electric load may be monitored and their values may betransmitted to the power outlet via the communications channel 6120. Aprocessor in the power outlet may then calculate the requiredtransmission frequency directly.

The method described here above, refers to a non-resonant transmissionfrequency lying within the linear region 8 (FIG. 6b ), higher than theresonant peak 2. It will be appreciated however that in alternativeembodiments frequency controlled power regulation may be achieved whenthe transmission frequency lies in the lower linear region 6 of theresonance curve. Nevertheless, as explained below, for certainembodiments, the selection of transmission frequencies in the higherlinear 8 may be preferred.

As described above, the resonant frequency f_(R) of an inductive coupleis given by the formula

${f_{R} = \frac{1}{2\pi\sqrt{LC}}},$where L is the inductance of the system and C is the capacitance of thesystem. Thus any decrease in either the inductance L or the capacitanceC of the system thereby increases its resonant frequency.

In inductive power outlets transmitting at frequencies above the normalresonant frequency of the system, an increase in resonant frequency ofthe system causes a large increase in the transmission voltage. Inpreferred embodiments, a peak detector 6140 (FIG. 1) is be provided tomonitor the transmission voltage of the power outlet 6200 and isconfigured to detect large increases in the transmission voltageindicating an increase in resonant frequency. Such increases intransmission voltage may be indicative of power drains, short circuits,removal of the secondary unit or the like.

As an example of the use of a peak detector reference is again made toFIG. 6c . It will be appreciated that in a desktop environment,conductive bodies such as a paper clip, metal rule, the metal casing astapler, a hole-punch or any metallic objects may be introduced betweenthe inductive power outlet 6200 and the secondary power receiving unit6300. The oscillating magnetic field produced by the primary coil 6220would then produce eddy currents in the conductive body heating it andthereby draining power from the primary coil 6220. Such a power drainmay be wasteful and/or dangerous.

Power drains such as described above reduce the inductance L of thesystem. The inductance L may also be reduced by the removal of thesecondary coil 6220, a short circuit or the like. A peak detector 6140,wired to the inductive power outlet, would detect any of these scenariosas a large increase in transmission voltage. Preferably, the powertransfer system may be further configured to shut down, issue a warningor otherwise protect the user and the system in the event that the peakdetector 6140 detects such an increase in transmission voltage.

FIG. 6e is a circuit diagram of an inductive power outlet 6200 and asecondary unit 6300. The secondary unit 6300 comprises a secondary coil6320 wired to an electric load 6340 via a rectifier 6330.

The inductive power outlet 6200 comprises a primary coil 6220 driven bya half-bridge converter 6230 connected to a power source 6240. Thehalf-bridge converter 6230 is configured to drive the primary coil 6220at a frequency higher than the resonant frequency of the system and apeak detector 6140 is configured to detect increases in the transmissionvoltage.

Although only a half-bridge converter is represented in FIG. E6, it isnoted that other possible driving circuits include: a DC-to-DCconverter, an AC-to-DC converter, an AC-to-AC converter, a flybacktransformer, a full-bridge converter, a flyback converter or a forwardconverter for example.

Thus, by using a transmission voltage oscillating at a frequencydifferent from the resonant frequency of the system, the inductivetransfer system has a higher tolerance to environmental fluctuations andvariations in inductive coil alignment than other transfer systems andthe frequency may be used to regulate power transfer. Moreover, when thetransmission frequency is higher than the resonant frequency of thesystem, a peak detector may be used to indicate hazards.

Inductive Communication Channel

U.S. Pat. No. 5,455,466 titled, “Inductive coupling system for power anddata transfer” to Terry J. Parks and David S. Register describes asystem for inductively coupling power and data to a portable electronicdevice. The portable device, such as a personal digital assistant (PDA),is powered or recharged via an inductive link between the device and asupport unit. The same inductive link is also used to transfer datasignals between the device and a second electronic device, such as aconventional desktop computer. The support unit includes a primarywinding of a transformer, a power amplifier and a modulator. Theportable device includes a secondary winding connected in parallel withthe input of a rectifier, the output of which is connected to a batterycharging circuit, and to a modem, which is further connected to thedevice microprocessor. Placement of the device on the support uniteffects the inductive coupling when the primary and secondary windingsare in proximity to one another. Parks' system is thus directed toproviding a data channel for synchronizing two data storage devices forexample a PDA and a computer.

In Parks' system data transfer from the primary winding to the secondarywinding may be provided by modulating the power signal. This requires aseparate data signal to be transmitted by the secondary winding which isinduced in the primary winding. Power transmission must therefore beinterrupted in order to transmit data signals from the secondary windingto the primary winding. As a result, Parks' system does not offer anysolution to providing a feedback signal for the regulation ofuninterrupted inductive power transfer to an electric load.

Reference is now made to FIG. 7a showing a block diagram of the mainelements of an inductive power transfer system 7100 consisting of aninductive power outlet 7200 configured to provide power to a remotesecondary unit 7300. The inductive power transfer system 7100 includesan inductive communication channel 7120 according to a furtherembodiment of the present invention. The communication channel 7120 isconfigured to produce an output signal S_(out) in the power outlet 7200when an input signal S_(in) is provided by the secondary unit 7300without interrupting the inductive power transfer from the outlet 7200to the secondary unit 7300.

The inductive power outlet 7200 includes a primary inductive coil 7220wired to a power source 7240 via a driver 7230. The driver 7230 isconfigured to provide an oscillating driving voltage to the primaryinductive coil 7220, typically at a voltage transmission frequency f_(t)which is higher than the resonant frequency f_(R) of the system.

The secondary unit 7300 includes a secondary inductive coil 7320, wiredto an electric load 7340, which is inductively coupled to the primaryinductive coil 7220. The electric load 7340 draws power from the powersource 7240. Where the electric load 7340 requires a direct currentsupply, for example a charging device for an electrochemical cell or thelike, a rectifier 7330 may be provided to rectify the alternatingcurrent signal induced in the secondary coil 7320.

An inductive communication channel 7120 is provided for transferringsignals from the secondary inductive coil 7320 to the primary inductivecoil 7220 concurrently with uninterrupted inductive power transfer fromthe primary inductive coil 7220 to the secondary inductive coil 7320.The communication channel 7120 may provide feedback signals to thedriver 7230.

The inductive communication channel 7120 includes a transmission circuit7122 and a receiving circuit 7124. The transmission circuit 7122 iswired to the secondary coil 7320, optionally via a rectifier 7330, andthe receiving circuit 7124 is wired to the primary coil 7220.

The signal transmission circuit 7122 includes at least one electricalelement 7126, selected such that when it is connected to the secondarycoil 7320, the resonant frequency f_(R) of the system increases. Thetransmission circuit 7122 is configured to selectively connect theelectrical element 7126 to the secondary coil 7320.

As known, the resonant frequency f_(R) of an inductive couple is givenby the formula

${f_{R} = \frac{1}{2\pi\sqrt{LC}}},$where L is the inductance of the system and C is the capacitance of thesystem. Thus any decrease in either the inductance L or the capacitanceC increases the resonant frequency of the system. The electrical element7126 may be a low resistance for example, typically the resistance ofthe electrical element 7126 is under 50 ohms and preferably about 1 ohm.

The signal receiving circuit 7124 may include a voltage peak detector7128 configured to detect large increases in the transmission voltage.In systems where the voltage transmission frequency f_(t) is higher thanthe resonant frequency f_(R) of the system, such large increases intransmission voltage may be caused by an increase in the resonantfrequency f_(R) thereby indicating that the electrical element 7126 hasbeen connected to the secondary coil 7320. Thus the transmission circuit7122 may be used to send a signal pulse to the receiving circuit 7124and a coded signal may be constructed from such pulses.

According to some embodiments, the transmission circuit 7122 may alsoinclude a modulator (not shown) for modulating a bit-rate signal withthe input signal S_(in). The electrical element 7126 may then beconnected to the secondary inductive coil 7320 according to themodulated signal. The receiving circuit 7124 may include a demodulator(not shown) for demodulating the modulated signal. For example thevoltage peak detector 7128 may be connected to a correlator forcross-correlating the amplitude of the primary voltage with the bit-ratesignal thereby producing the output signal S_(out).

In other embodiments, a plurality of electrical elements 7126 may beprovided which may be selectively connected to induce a plurality ofvoltage peaks of varying sizes in the amplitude of the primary voltage.The size of the voltage peak detected by the peak detector 7128 may beused to transfer multiple signals.

FIG. 7b is a graph showing how the amplitude of the operational voltagevaries according to the transmission frequency. It is noted that thevoltage is at its highest when the transmission frequency is equal tothe resonant frequency f_(R) of the system, this maximum amplitude isknown as the resonance peak 2. If the resonant frequency f_(R) of thesystem increases, a new resonance peak 2′ is produced.

According to an exemplary embodiment of the invention, an inductivepower transfer system 7100 operates at a given transmission frequencyf_(t) which is higher than the resonant frequency f_(R) of the system.The normal operating voltage V_(t) is monitored by the voltage peakdetector 7128. When the electric element 7126 is connected to thesecondary inductive coil 7320 the resonant frequency of the systemincreases. Therefore, the operating voltage increases to a higher valueV_(t)′. This increase is detected by the voltage peak detector 7128.

The present invention allows data signals to be transferred from thesecondary coil 7320 to the primary coil 7220 concurrently with inductivetransfer of power from the primary coil 7220 to the secondary coil 7320.Consequently, the signal transfer system may be used to provide feedbacksignals for real time power regulation. This is in contradistinction toprior art inductive signal transfer systems, such as the systemdescribed in U.S. Pat. No. 5,455,466 titled, “Inductive coupling systemfor power and data transfer” to Terry J. Parks and David S. Register, inwhich a separate data signal is supplied to the secondary inductive coilsuch that a voltage is induced in the primary coil.

FIG. 7c shows an exemplary circuit diagram of an inductive power outlet7200 and a secondary unit 7300, according to another embodiment of theinvention. An inductive feedback channel 7120 is provided fortransferring signals between the coils concurrently with uninterruptedinductive power transfer.

The inductive power outlet 7200 comprises a primary coil 7220 driven bya half-bridge converter 7230 connected to a power source 7240. Thehalf-bridge converter 7230 is configured to drive the primary coil 7220at a frequency higher than the resonant frequency of the system. Thesecondary unit 7300 comprises a secondary coil 7320 wired to the inputterminals T₁, T₂ of a rectifier 7330, and an electric load 7340 wired tothe output terminals T₃, T₄ of the rectifier 7330.

Although only a half-bridge converter 7230 is represented in theinductive power outlet 7200 of FIG. 7c , it is noted that other drivingcircuits could be used. These include: a DC-to-DC converter, an AC-to-DCconverter, an AC-to-AC converter, a flyback transformer, a full-bridgeconverter, a flyback converter or a forward converter for example.

The inductive feedback channel 7120 comprises a transmission circuit7122, in the secondary unit 7300 and a receiving circuit 7124 in theinductive power outlet 7200. The transmission circuit 7122 comprises anelectrical resistor 7126 connected to the rectifier 7330 via a powerMOSFET switch 7125. A modulator 7123 may provide an input signal S_(in)to the power MOSFET 7125.

It is noted that in this embodiment the transmission circuit 7122 iswired to one input terminal T₁ and one output terminal T₃ of therectifier 7330. This configuration is particularly advantageous as, evenwhen the transmission circuit 7122 is connected, the resistor 7126 onlydraws power from the system during one half of the AC cycle, therebysignificantly reducing power loss.

The receiving circuit 7124 includes a voltage peak detector 7128 that isconfigured to detect increases in the transmission voltage, and ademodulator 7129 for producing an output signal S_(out).

With reference now to FIG. 7d , a flowchart is presented showing themain steps in a method for transferring a signal from the secondaryinductive coil to a primary inductive coil of an inductive powertransfer system. The method includes the following steps:

-   -   Step (a)—connecting the primary inductive coil to a voltage        monitor for monitoring the amplitude of a primary voltage across        the primary coil;    -   Step (b)—connecting the secondary inductive coil to a        transmission circuit for connecting an electric element to the        secondary inductive coil thereby increasing the resonant        frequency of the inductive power transfer system;    -   Step (c)—providing an oscillating voltage to the primary        inductive coil at an initial transmission frequency higher than        the resonant frequency thereby inducing a voltage in the        secondary inductive coil;    -   Step (d)—using the transmission circuit to modulate a bit-rate        signal with the input signal to create a modulated signal and        connecting the electrical element to the secondary inductive        coil intermittently according to the modulated signal;    -   Step (e)—using the voltage monitor to cross-correlate the        amplitude of the primary voltage with the bit-rate signal for        producing an output signal.

The inductive feedback channel 7120 may be used for transferring data,such as data pertaining to any or all of the following:

-   -   the required operating voltage, current, temperature or power        for the electric load 7240    -   the measured voltage, current, temperature or power supplied to        the electric load 7240 during operation    -   the measured voltage, current, temperature or power received by        the electric load 7240 during operation and the like    -   identification data for the user, electronic device and such        like    -   a release signal of a transmission-key for releasing a        transmission-lock.

Therefore, the inductive communication channel may be used to transfer afeedback signal from the secondary inductive coil to the primaryinductive coil for regulating power transfer across an inductive powercoupling.

For example the system may be configured to transfer two signals withthe driver being configured to decrease the transmission power when afirst signal is received, and to increase the transmission power when asecond signal is received.

Power may be regulated by altering the duty cycle of the transmissionvoltage provided by the driver. Furthermore, the driver 7230 may beconfigured to adjust the transmission frequency in order to regulate thepower transfer, as described hereinabove. Accordingly, the driver may beconfigured to adjust the transmission frequency in response to feedbacksignals. The transmission frequency may be increased when the firstsignal is received thereby decreasing the operating voltage, and thetransmission frequency may be decreased when the second signal isreceived, thereby increasing the operating voltage.

Thus a communication channel is provided for regulating power transferand/or for transmitting data signals from the secondary coil to theprimary coil of an inductive couple while power is being transferred.

It will be apparent from the above description that various embodimentof the present invention disclose significant advantages enabling theefficient, safe and unobtrusive inductive transfer of power. It isfurther noted that, in combination, these advantages allow an inductivepower transmission system to become a practical tool suitable for avariety of applications.

The scope of the present invention is defined by the appended claims andincludes both combinations and sub combinations of the various featuresdescribed hereinabove as well as variations and modifications thereof,which would occur to persons skilled in the art upon reading theforegoing description.

In the claims, the word “comprise”, and variations thereof such as“comprises”, “comprising” and the like indicate that the componentslisted are included, but not generally to the exclusion of othercomponents.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A wireless power transmitter operable to transferpower wirelessly to a wireless power receiver, said wireless powertransmitter comprising: a primary coil operable to form an inductivecouple with a secondary coil associated with said wireless powerreceiver and to transfer power wirelessly thereto; a detector operableto activate said wireless power transmitter when a wireless powerreceiver is brought into proximity therewith; a driver operable to betriggered by said detector and to provide a driving voltage across saidprimary coil; and a peak detector for monitoring transmission voltage ofsaid wireless power transmitter, wherein said detector is operable todetect resonance of said inductive couple, said driver is operable toselect a transmission frequency significantly different from a resonantfrequency of said inductive couple, and said peak detector is configuredto detect large increases in the transmission voltage indicating anincrease in resonant frequency.
 2. The wireless power transmitter ofclaim 1 wherein said detector comprises an array of magnetic switches.3. The wireless power transmitter of claim 2, wherein said array ofmagnetic switches is configured to be activated by a correspondingconfiguration of magnetic elements in the wireless power receiver. 4.The wireless power transmitter of claim 1 wherein said detectorcomprises a Hall effect sensor configured to detect a magnetic field. 5.The wireless power transmitter of claim 1 wherein said detectorcomprises a magnetic switch.
 6. The wireless power transmitter of claim1 wherein said detector comprises said primary coil.
 7. The wirelesspower transmitter of claim 1 wherein said detector is operable to detectresonance of said wireless power receiver.
 8. The wireless powertransmitter of claim 1 wherein said detector is operable to detect afrequency identifying the wireless power receiver.
 9. The wireless powertransmitter of claim 1 wherein said detector is operable to detect afrequency authenticating the wireless power receiver.
 10. The wirelesspower transmitter of claim 1 wherein said primary coil is operable toapply a power pulse to energize said secondary coil to transmit aresponse signal and said detector is operable to detect said responsesignal.
 11. A method for establishing wireless power transfer from awireless power transmitter to a wireless power receiver, which methodcomprises: detecting, by a detector of said wireless power transmitter,a magnetic field when said wireless power receiver is in proximitytherewith; activating said wireless power transmitter upon detection ofthe magnetic field; detecting resonance of an inductive couple formedbetween a primary coil of said wireless power transmitter and asecondary coil of said wireless power receiver; selecting a transmissionfrequency significantly different from a resonant frequency of saidinductive couple; and monitoring transmission voltage of said wirelesspower transmitter to detect large increases in the transmission voltage.12. The method of claim 11 wherein said detecting comprises a Halleffect sensor detecting a magnetic field from said wireless powerreceiver.
 13. The method of claim 11 wherein said detecting comprisessaid primary coil detecting a response from a secondary coil of saidwireless power receiver.
 14. The method of claim 11 wherein saiddetecting comprises said primary coil detecting a frequencyauthenticating the wireless power receiver.
 15. The method of claim 11wherein said detecting comprises said primary coil applying a powerpulse to energize a secondary coil of said wireless power receiver totransmit a response signal and said detecting said response signal.